Jul. 05, 2012

We've got friends in cool places. This photo of a male red headed mouse spider was taken by our friend Bridie Campbell in Warrambungles National Park in New South Wales, Australia. For Kristie, this spider is #1 on her "Top 5 Spiders To See Down Under" list. Sadly, she missed it last year while traveling in NSW but we thought we'd share this photo and take the opportunity to teach about some of the cool morphological features these spiders and their relatives have.

Some terminology:

Arachnid: an arthropod with four pair of legs and two body sections and chelicerate mouthparts.

Chelicerae - a pair of oral appendages or jaws modified as fangs on spiders

Cephalothorax - the fused head and thorax of an arachnid (and other arthropods like crustaceans)

Opisthosoma - the abdomen of a spider

Mouse spiders (along with trap door spiders and tarantulas) are mygalomorphs. This means they are primitive with chelicerae that are orthognathus. That's an intense word. Orthognathous literally means "straight-jawed." The fangs stab downwards as opposed to towards each other. This is different from the spiders people commonly see, like orb weavers, which are araneomorphs. Mygalomorphs have four book lungs in the opithosoma whereas most aranemorphs only have the front pair. Book lungs are breathing organs that are filled with many layered tissues that lie like the pages of a book. Book lungs are internal structures, but often you can see evidence of them on the underside of a spider.

The red headed mouse spider is found all over Australia. It's rare to see a female mouse spider, as they stay in their burrows throughout the year. This male was most likely on the hunt for a female. These spiders are sexually dimorphic. This means that male and females have different body forms. Males, like the one shown in the picture above have a distinctive raised area on the cephalothorax directly behind the chelicerae. Its bright red and their abdomens are a bluish-black. Like most spiders there is a very obvious size difference between males and females. Males have longer, more slender legs with slender abdomens and females are usually much larger, with shorter, stouter legs and bulbous abdomens. There are some fantastic pictures on the Australian Museum's website along with great information. Check out the females!

Interested to see what was on Kristie's list for Australian Spiders? She saw and photographed all but two:

We have a lot of "Top 5" lists--countries, habitats, and of course arthropods. Kristie has a Top 5 list for just about every category of animal so that she can see as many species as possible. We'd love to hear about your Top 5 lists!

Many thanks to Bridie Campbell and Hugh Ward of Aussie 7 Summits for their photos!